licheer
关于界面设置windows风格报错的问题～～～
小菜开发了一个接口，想把界面设置成windows风格的。
于是使用了下面这些语句：
UIManager.setLookAndFeel(UIManager.getSystemLookAndFeelClassName());
SwingUtilities.updateComponentTreeUI(jPlCenter_1);
然后它就开始时不时的报下面这个错，但是并不是每次都报错，且不影响功能使用。
其中有一个combox的组件，但是我已经使用setselectedindex(0)设置默认值了啊。。
java.lang.NullPointerException
at javax.swing.plaf.basic.BasicComboBoxUI.paintCurrentValue(BasicComboBoxUI.java:1156)
at javax.swing.plaf.basic.BasicComboBoxUI.paint(BasicComboBoxUI.java:954)
at javax.swing.plaf.ComponentUI.update(ComponentUI.java:142)
at javax.swing.JComponent.paintComponent(JComponent.java:541)
at javax.swing.JComponent.paint(JComponent.java:808)
at javax.swing.JComponent.paintChildren(JComponent.java:647)
at javax.swing.JComponent.paint(JComponent.java:817)
at javax.swing.JComponent.paintWithOffscreenBuffer(JComponent.java:4787)
at javax.swing.JComponent.paintDoubleBuffered(JComponent.java:4740)
at javax.swing.JComponent._paintImmediately(JComponent.java:4685)
at javax.swing.JComponent.paintImmediately(JComponent.java:4488)
at javax.swing.RepaintManager.paintDirtyRegions(RepaintManager.java:410)
at javax.swing.SystemEventQueueUtilities$ComponentWorkRequest.run(SystemEventQueueUtilities.java:117)
at java.awt.event.InvocationEvent.dispatch(InvocationEvent.java:178)
at java.awt.EventQueue.dispatchEvent(EventQueue.java:454)
at java.awt.EventDispatchThread.pumpOneEventForHierarchy(EventDispatchThread.java:201)
at java.awt.EventDispatchThread.pumpEventsForHierarchy(EventDispatchThread.java:151)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:145)
at java.awt.EventDispatchThread.pumpEvents(EventDispatchThread.java:137)
at java.awt.EventDispatchThread.run(EventDispatchThread.java:100)
其中最上面的错误，点击进去的时候是下面这段代码：
即这个错误at javax.swing.plaf.basic.BasicComboBoxUI.paintCurrentValue(BasicComboBoxUI.java:1156)
对应代码如下：
c = renderer.getListCellRendererComponent( listBox,
comboBox.getSelectedItem(),
-1,
false,
false );
各位大侠帮忙看看，到底是什么问题，需要做哪些修改？